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Refractory materials configuration and erosion mechanisms in blast furnaces
2026-03-16
The longevity of a blast furnace primarily depends on the following factors: furnace structure design, selection of refractory materials, matching and quality of cooling equipment, production operations, and lining repair. Especially in the middle and later stages of blast furnace operation, the furnace lining will experience a certain degree of damage, thus affecting the safe operation of the blast furnace. Therefore, reasonable and effective blast furnace maintenance techniques are one of the key measures for achieving blast furnace longevity. The configuration of refractory materials in the blast furnace itself is one of the important factors affecting blast furnace longevity; at the same time, a thorough understanding of the refractory material configuration of the blast furnace is the basis for selecting or developing targeted blast furnace refractory lining maintenance techniques.
1. The furnace body and middle section are made of refractory materials.
The working environment temperature in the upper and middle sections of the furnace is relatively low, and there is no slag formation or slag corrosion. However, these sections are subjected to abrasion from solid materials, erosion from high-temperature gas streams, and a certain degree of chemical corrosion. Therefore, the linings in the upper and middle sections of the furnace often use high-quality clay bricks with low porosity and high-alumina bricks, or even phosphate-bonded clay bricks or sillimanite refractory bricks with good spalling resistance and wear resistance.
2. Refractory Materials for the Lower Part of the Furnace Body
Two main approaches have coexisted regarding the selection of refractory materials for the lower part of the blast furnace body. The refractory materials school of thought believes that the damage to the refractory materials in the lower part of the furnace body is mainly caused by high-temperature wear and chemical erosion. Therefore, they recommend using high-quality aluminum silicate and silicon carbide products with low thermal conductivity, high strength, and strong corrosion resistance, such as corundum and Sialon-bonded SiC bricks. The thermodynamics school of thought believes that temperature fluctuations are the main factor causing damage to the blast furnace lining, and suggests using an efficient cooling system and selecting high-thermal conductivity materials such as carbon and graphite as lining materials to reduce the hot surface temperature of the furnace lining and resist high-intensity thermal shock; at the same time, promoting the formation of a slag protective layer to extend the service life of the refractory lining.
3. Refractory Materials for the Hearth and Bosh
The hearth, bosh, and lower part of the furnace body are key areas where materials react with each other inside the blast furnace. These areas are subjected to material abrasion, erosion by hot gas flow, attack by harmful elements, and corrosion by molten materials. Therefore, the refractory materials used in these areas must possess excellent corrosion resistance, oxidation resistance, alkali resistance, high thermal conductivity, thermal shock resistance, and wear resistance.
4. Refractory Materials for Hearth and Bottom of Blast Furnace
The refractory materials for the hearth and bottom of the blast furnace are subjected not only to high temperatures but also to chemical erosion by slag and molten iron, as well as severe corrosion by alkalis and zinc. Therefore, the refractory materials for the hearth and bottom need to possess excellent corrosion resistance, permeability, and alkali resistance. Currently, the main structures used for the hearth and bottom of blast furnaces domestically and internationally are all-carbon and carbon-ceramic composite structures.
The all-carbon material structure aims to achieve thermal equilibrium by rapidly transferring heat to the cooling system using semi-graphitic carbon blocks with high thermal conductivity. This also helps to lower the working surface temperature, promote the formation of slag crust, and push the 800℃ isotherm outside the carbon bricks, ensuring the safety and longevity of the hearth system.
The carbon-ceramic composite structure design, while agreeing with the all-carbon material structure design, believes that adding a ceramic cup made of ceramic materials with good corrosion resistance, erosion resistance, and thermal shock resistance, separates the carbonaceous material in the hearth from the molten iron and other mixtures. This can prevent the erosion of the carbonaceous material hearth by molten iron for a period of time, achieving safe, efficient, and long-lasting operation of the hearth system.
No. 2 Erosion Mechanisms of Refractory Materials in Blast Furnaces
During the descent of materials in the blast furnace, continuous heat exchange occurs, leading to variations in temperature, pressure, and atmosphere within the furnace. Consequently, the damage mechanisms of refractory materials differ in different parts of the furnace. The erosion mechanisms and their approximate proportions for blast furnace lining refractory materials are as follows: alkali metal erosion accounts for 40%; oxidation by CO, H2O, etc., accounts for 20%; wear resistance accounts for 10%; poor thermal conductivity accounts for 10%; thermal shock damage accounts for 15%; and slag erosion accounts for 5%. In fact, the damage to the blast furnace lining is the result of the combined effects of several erosion factors.
The upper part of the blast furnace lining experiences the most severe wear, while the hearth, bosh, and lower part of the furnace body experience the most severe erosion. The hearth, bosh, and middle and lower parts of the furnace body are mainly subjected to erosion from three aspects: scouring by high-temperature gas and molten iron, high heat flux intensity and thermal shock, and damage from alkali metals and zinc. Among these, the damage caused by alkali metals and zinc is the greatest, followed by thermal shock damage and wear, with slag erosion being the least significant.
In recent years, to improve the utilization coefficient of blast furnaces, the temperature of molten iron has increased, leading to more severe damage to the refractory lining of the hearth, especially in the taphole area and the abnormally eroded areas below the taphole, which have become critical areas limiting the lifespan of the blast furnace.
The central part of the blast furnace bottom experiences more erosion, easily forming a "pot-bottom" shape of erosion. The shape of hearth erosion is often "elephant's foot" shaped. The reasons for this abnormal erosion include: firstly, molten iron penetration and its circulation cause changes in the carbon brick structure and wear; secondly, alkali erosion on the 800℃ isotherm inside the carbon bricks, and the reaction of gases with alkali metals, generating carbonate deposits in the carbon bricks, which then react with carbon. As production continues, this reaction continues, ultimately forming a brittle layer. The reaction equations are:
2K(g) + 2CO2(g) = K2CO3(l) + CO(g) (1)
K2CO3(l) + 2C(s) = K(g) + 3CO(g) (2)
Therefore, when selecting refractory materials for the hearth and bottom of the furnace, materials with excellent comprehensive properties should be chosen or developed based on the above mechanisms. Simultaneously, a composite hearth structure should be considered, using dense refractory materials for the working layer to improve resistance to molten iron penetration and alkali corrosion, and high-thermal-conductivity materials near the cooling wall.